1. Field of the Invention
The invention relates to an input and/or output device for process data. The device includes a mounting rack and at least one module fastened on the mounting rack. A process connector can be inserted into the at least one module on the front side thereof. The at least one module has at least one circuit board which is located in a housing and is electroconductively connected to a process connector and to a bus connector, as well as a terminal strip. The at least one circuit board is connected non-positively to the process connector, for receiving contact pins which interact with contacts of the process connector.
Such input and/or output devices have modules which are fastened on a mounting rack and are connected via process connectors and cables to a device for executing a process. The modules communicate with one another via a system bus. Each of the modules include at least one circuit board located in a housing. The modules pick up signals from signal transmitters of a process execution device, process the signals, taking signals output by other modules into account if appropriate, and/or feed signals to signal receivers of the process execution device. Depending on requirements, a module may perform input, output, input and output and/or processing functions. The features of the device are essentially determined by the functions of the individual modules. The device, and hence in particular also each individual module, must not be damaged by the effects of electromagnetic interference, nor must its functioning be impaired. This is generally achieved by diverting usually high-frequency interference currents flowing toward the device to ground by means of protective devices before the interference currents enter circuits provided in one of the modules. The circuits are protected against the coupling-in of non-line-related interference by a shielding device.
2. Discussion of Background
An input and/or output device of the type mentioned above is known, for example, from EP-A-165 434. In this device, or in comparable devices, the housings of the modules are usually made of plastic. Unwanted interference currents introduced into a module via the process connector are conducted by conductor tracks arranged on the circuit board, or by a ground wire inserted into the housing of the module, from the signal input on the front side to a ground terminal of the module in contact with the mounting rack. It is customary for additional metal coatings or insertion plates to be provided on the housing. As a result of these measures, circuits provided on the circuit board are shielded from unwanted electromagnetic radiation, and consequently the full functioning of the circuits is maintained.